1. Field of the Invention
The present invention relates to a rotary drive system, more precisely relates to a rotary drive system for simultaneously rotating a plurality of output shafts.
2. Description of Background Art
The rotary drive system for simultaneously rotating a plurality of output shafts is used for, for example, a multi-head screwing device, which is capable of simultaneously screwing a plurality of bolts. The multi-head screwing device has a plurality of rotary heads, which are respectively attached to rotatable output shafts, for screwing bolts. The output shafts are respectively rotated by motors, or one motor with a gear transmitting mechanism.
By simultaneously rotating the output shafts and the rotary heads in the same direction at the same speed, a plurality of bolts can be screwed in the same manner.
However, the multi-head screwing device has some disadvantages.
Firstly, in case of using a plurality of motors for rotating the output shafts, all motors must be rotated in the same manner. But it is practically impossible to rotate all motors in the same manner because performance of the motors cannot be equal.
Secondly, in case of using one motor with the gear transmitting mechanism, the number of gear between the motor and each output shaft is mutually different, so mutual time lag of transmitting torque from the motor to each output shaft cannot be avoided. Thus, it is practically impossible to rotate all output shafts in the same manner.
If all output shafts do not rotate in the same manner, the bolts cannot be screwed in the same manner.